JPH0463028B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for manufacturing a silicon carbide sintered body,
In particular, the present invention relates to a method for manufacturing a silicon carbide sintered body having excellent oxidation resistance. Silicon carbide has chemical and physical properties such as high strength, good wear resistance, good oxidation resistance, good corrosion resistance, good thermal conductivity, low coefficient of thermal expansion, high thermal shock resistance and high strength at high temperatures. It has excellent physical properties and is a wear-resistant material for mechanical seals, bearings, etc.
It is a material that can be widely used as a refractory material for high-temperature furnaces, a heat-resistant structural material for heat exchangers, combustion tubes, etc., and a corrosion-resistant material for pump parts for highly corrosive solutions such as acids and alkalis. [Prior Art] By the way, silicon carbide is conventionally known as a material that is difficult to sinter. In other words, until recently, it has been difficult to obtain a high-density sintered body of this material using the pressureless sintering method, which is generally used to produce oxide ceramics, in which the material is molded at room temperature and then sintered under no pressure. It was hot. However, recently, various pressureless sintering methods have been proposed in which a mixed powder consisting of silicon carbide powder and sintering aids such as boron-containing additives and carbonaceous additives is compacted and sintered in an inert atmosphere. ing. For example, according to the invention described in JP-A-50-78609, (a) silicon carbide, a boron-containing compound in an amount corresponding to 0.3 to 3.0% by weight of boron, and
and a carbonaceous additive in an amount corresponding to 0.1 to 1.0% by weight of carbon; (b) forming the powder mixture into a green body; c) 1900~2100 of the raw object
A method of making a high-density silicon carbide ceramic is disclosed which includes sintering in an inert atmosphere at a temperature of 0.degree. C. for a time sufficient to obtain a ceramic article having a density of at least 85% of the theoretical density. According to the invention described in JP-A-54-67599,
Organosilicon polymer compounds whose main skeleton components are silicon and carbon are heated to 1600 ~
Pyrolysis is performed at a temperature of 2200°C to obtain a powder mainly composed of β-SiC, which is heated in an oxidizing atmosphere to a temperature of 500 to 800°C, and then treated with an acid containing at least hydrofluoric acid. Impurities are dissolved and removed to obtain a powder made of high-purity β-SiC, and carbon and boron are added to the raw material powder using this powder until the content of each in the mixture becomes 0.1 to 5% by weight. After forming into the specified shape, heat at 2000 to 2300℃ in vacuum, CO gas atmosphere, or inert gas atmosphere.
A method for producing a sintered silicon carbide body is disclosed, which comprises sintering at a temperature of at least 2.60 g/cm 3 for a time sufficient to achieve a density of at least 2.60 g/cm ³ or more. According to the invention described in JP-A-56-169181,
In a method for producing a silicon carbide sintered body in which silicon carbide fine powder, a boron-containing additive, and a carbonaceous additive are mixed, molded, and then sintered without pressure,
100 parts by weight of silicon carbide fine powder consisting essentially of 85% by weight or more and the remainder being 2H-type crystalline silicon carbide, a boron-containing additive of 0.1 to 3.0 parts by weight, and fixed carbon content in terms of boron content. A first step of homogeneously mixing more than 1.0 parts by weight and not more than 4.0 parts by weight of a carbonaceous additive; a second step of molding the homogeneous mixture into an arbitrary formed body; The third step is sintering at 2050 to 2200°C in a gas atmosphere consisting of at least one selected from krypton, xenon, and hydrogen.
Process: A high-strength product consisting of a combination of steps 1 to 3 above, containing 50 to 85% by weight of β-type crystals, more than 1.0% by weight and less than 3.0% of residual free carbon, and having a density of 3.0g/cm ³ or more. A method for manufacturing a silicon carbide sintered body is disclosed. [Problems to be Solved by the Invention] According to the invention described in JP-A-50-78609, boron is used as a sintering aid in a relatively large amount of 0.3 to 3.0% by weight based on silicon carbide. Because of the presence of oxidation, the resulting sintered body has a disadvantage of poor oxidation resistance. Furthermore, according to the invention described in JP-A-54-67599, the extremely expensive β-SiC powder obtained by thermally fielding an organosilicon polymer compound is used as a starting material, so it can be used as an industrial material. The disadvantage is that it is difficult to widely use. The invention described in JP-A-56-169181 is an invention filed by the applicant, and its purpose is to improve the pressureless sintering method of silicon carbide and to obtain a high-strength sintered body. By adding the quality additive in excess of the amount required depending on the oxidation content of the silicon carbide fine powder and actively incorporating it in the form of free carbon into the silicon carbide sintered body, β-type crystals can be formed. The phase transformation to the α-type crystal is optimized, and the β-type crystal becomes coarse and fine crystals as it changes to the α-type. However, in order to obtain a high-strength sintered body, the invention described in the above publication requires silicon carbide containing 85% by weight or more of β-type crystals as a starting material, and the amount of boron and carbon added as sintering aids. However, it has the disadvantage of being subject to various restrictions. The present invention eliminates the drawbacks of the previously known pressureless sintering methods for silicon carbide as described above, and is particularly suitable for use under harsh conditions such as gas turbine parts, high temperature heat exchangers, and furnace structural materials. It is an object of the present invention to provide a method that can inexpensively and easily produce a pressureless sintered body of silicon carbide having high density and excellent oxidation resistance. [Means for Solving the Problem] According to the present invention, in a method for producing a silicon carbide sintered body in which fine silicon carbide powder is sintered without pressure, β-type carbide having an average crystal lattice constant of 4.3584 Å or more is used. silicon
100 parts by weight of silicon carbide fine powder containing 50% by weight or more, a boron-containing additive of 0.01 to 0.25 parts by weight in terms of boric acid content, and 0.3 to 0.3 parts by weight in terms of fixed carbon content.
After homogeneously mixing with 5.0 parts by weight of carbonaceous additive, it is molded into a formed body having an arbitrary shape, and then sintered at 1700-2300°C in a non-oxidizing atmosphere to produce 2.8 g/
The above object can be achieved by a method for producing a silicon carbide sintered body, which is characterized by producing a silicon carbide sintered body having a density of cm ³ or more. Next, the present invention will be explained in detail. Conventionally, according to a pressureless sintering method of silicon carbide, a sintered body is manufactured by mixing silicon carbide powder with boron and carbon and sintering the mixture. By the way, since the boron remains in the sintered body and lowers the melting point of the silica layer on the surface of the sintered body, thereby deteriorating the oxidation resistance of the sintered body, it is desirable that the amount added is as small as possible. However, according to the conventionally known pressureless sintering method for silicon carbide, some specific silicon carbide fine powders, such as the organosilicon polymer compound described in JP-A No. 54-67599, cannot be thermally decomposed. Extremely expensive β-type silicon carbide powder obtained by
Except for the silicon carbide fine powder that is substantially composed of 85% by weight or more of β-type crystals and the remainder of 2H-type crystals as described in the publication, high-density silicon carbide can be produced by pressureless sintering even with a small amount of boron added. It is difficult to obtain solids, and the minimum amount of boron added is
It was 0.1% by weight, which was not a very small amount. The present inventors have determined that the average value of the lattice constant of the crystal is
Silicon carbide fine powder, mainly composed of β-type silicon carbide with a diameter of 4.3584 Å or more, has extremely excellent sinterability, and by using it as a starting material in the pressureless sintering method,
It is possible to uniformly generate many nets between silicon carbide particles with an extremely small amount of boron added, and it is possible to obtain a silicon carbide sintered body that has a high density and uniform microstructure and has excellent oxidation resistance. We discovered something new. According to the present invention, the silicon carbide fine powder must contain 50% by weight or more of β-type silicon carbide having an average crystal lattice constant of 4.3484 Å or more.
The reason is that the average value of the lattice constant of the crystal is
β-type silicon carbide with a diameter of 4.3584 Å or more has extremely excellent sinterability, and by using silicon carbide fine powder containing 50% by weight or more of the β-type silicon carbide as a starting material, it can be sintered even with an extremely small amount of boron added. This is because a high-density sintered body can be obtained, and among them, silicon carbide fine powder containing 70% by weight or more is more advantageous. The β-type silicon carbide used in the present invention is a β-type silicon carbide obtained by firing silica and carbon at a high temperature as starting materials.
Type silicon carbide is preferable, and it is economically advantageous to use the manufacturing apparatus described in Japanese Patent Publication No. 57-48485, which is an invention previously filed by the present applicant. The reason why β-type silicon carbide with a crystal lattice constant of 4.3584 Å or more has excellent sintering properties is that β-type silicon carbide with a crystal lattice constant of 4.3584 Å or more has excellent sintering properties. This is thought to be due to the fact that there is a high probability that nets will be formed between particles during the formation of nets in the process, and that elements can easily diffuse through grain boundaries. The β-type silicon carbide whose crystal lattice constant has an average value of 4.3584 Å or more used in the present invention can be produced by dissolving aluminum as a solid solution during the silicon carbide production reaction, for example, by combining silica and carbon. It can be produced by firing at a high temperature range of 1,800 to 2,200°C using as a starting material an aluminum-containing additive added as necessary. Various aluminum-containing salts and metallic aluminum can be used as the aluminum-containing additive, but alumina (aluminum oxide),
It is advantageous to use mullite or the like. According to the present invention, the β-type silicon carbide preferably contains 0.02 to 1.0% by weight of aluminum. The reason for this is that if it is less than 0.02% by weight, it is difficult to make the crystal lattice constant larger than 4.3584 Å, while if it is more than 1.0% by weight, there will be a large amount of aluminum that will not be dissolved in silicon carbide, so the sintering This is because abnormal grain growth of plate-like crystals is likely to occur at times, which not only makes it difficult to obtain a high-density sintered body, but also deteriorates the high-temperature properties of the sintered body. % ranges are more advantageous. By the way, the present applicant previously disclosed the following invention in Japanese Unexamined Patent Publication No. 17465/1983. "In the method for manufacturing silicon carbide sintered bodies in which silicon carbide fine powder is sintered without pressure, aluminum is
100 parts by weight of silicon carbide fine powder containing 90% or more of silicon carbide in the form of β-type crystals, a boron-containing additive of 0.1 to 3.0 parts by weight in terms of boron content, and a boron-containing additive in terms of fixed carbon content. A first step of homogeneously mixing more than 1.0 parts by weight and not more than 4.0 parts of a carbonaceous additive; a second step of molding the homogeneous mixture into a formed body having an arbitrary shape; A third step of sintering at 1900 to 2100°C in a gas atmosphere consisting of at least one selected from krypton, xenon, and hydrogen;
80 to 95% of at least one type of 4H type crystal or 6H type crystal consisting of a combination of 3 steps, the remainder mainly consists of β type crystal, and residual free carbon is removed.
A method for producing a high-strength silicon carbide sintered body containing more than 1.0% by weight and less than 3.0% by weight and having a density of at least 3.0g/cm ³ . However, the invention described in the above publication uses silicon carbide fine powder containing 90% or more of β-type crystal silicon carbide as a starting material, and phase-transforms most of the crystals into α-type crystal silicon carbide during sintering. In contrast, the present invention produces a high-density silicon carbide sintered body containing 80 to 95% of β-type silicon carbide having an average crystal lattice constant of 4.3584 Å or more by 50% or more by weight. This is a method for producing a silicon carbide sintered body with high density and excellent oxidation resistance even with an extremely small amount of boron added by using the contained silicon carbide fine powder as a starting material, and it differs greatly in the purpose and structure of the invention. . According to the present invention, it is preferable that at least 20% by weight of the obtained silicon carbide sintered body is β-type silicon carbide. The reason for this is that if the amount of β-type silicon carbide contained in the obtained silicon carbide sintered body is less than 20% by weight, phase transformation during sintering will be significant, and abnormal grain growth of plate-like crystals will be noticeable due to phase transformation. This is because it is difficult to obtain a high-density sintered body. According to the present invention, the silicon carbide fine powder preferably has a specific surface area of 5 to 50 m ² /g. The reason for this is that when silicon carbide with a specific surface area smaller than 5 m ² /g is used as a starting material, there are fewer places where the necks are formed in the initial stage of sintering, and shrinkage during sintering becomes uneven. Silicon carbide fine powder with a specific surface area larger than 50 m ² /g has many places where necks occur and is considered to have excellent sinterability.
This is because such silicon carbide fine powder is difficult to obtain. According to the present invention, the silicon carbide fine powder preferably has an oxygen content of 0.1 to 1.0% by weight. Oxygen contained in the silicon carbide fine powder reacts with carbon during sintering and is removed by a mechanism as shown in the following equation. SiO ₂ +C→SiO+CO (1) SiO+2C→SiO+CO (2) Therefore, if the oxygen is present in an amount greater than 1.0% by weight, not only a large amount of carbonaceous additive must be used, but also a sintering aid. This is because sintering becomes difficult, such as when the boron as a material oxidizes or because a large amount of CO gas is generated, which requires degassing during sintering. On the other hand, the amount of oxygen is 0.1
Silicon carbide fine powder with less than 1% by weight can be obtained, for example, by treatment with a mixed acid of hydrofluoric acid and nitric acid, but the high purity silicon carbide fine powder obtained in this way is extremely active and cannot be used in an air atmosphere. This is because if the acid treatment is dried, it is easily oxidized even at room temperature, so in order to maintain a low oxygen content, the atmosphere after the acid treatment must be kept non-oxidizing, which is not practical. According to the present invention, the boron-containing additive is converted into boron content based on 100 parts by weight of silicon carbide fine powder.
It is necessary to add 0.01 to 0.25 parts by weight. The above boron-containing additive is converted into boron content.
The reason why it should be 0.01 to 0.25 part by weight is that if it is less than 0.01 part by weight, the adhesive effect during the formation of the net will be insufficient and it will be difficult to achieve high density. This is because the melting point of the silica layer on the surface of the sintered body is lowered and the oxidation resistance of the sintered body is deteriorated. As the boron-containing additive, it is preferable to use at least one selected from, for example, boron, boron carbide, or a mixture thereof. According to the present invention, a silicon carbide sintered body particularly excellent in oxidation resistance can be obtained when the amount of the boron-containing additive added is less than 0.1 part by weight in terms of boron content. According to the present invention, the carbonaceous additive is added to 100 parts by weight of silicon carbide fine powder in terms of fixed carbon content.
It is necessary to add 0.3 to 5.0 parts by weight. The carbonaceous additive is used to remove oxygen contained in the silicon carbide fine powder and to be interposed between the silicon carbide particles to optimize the diffusion of SiC. Therefore, it is advantageous to add the carbonaceous additive at least in an amount matching the oxygen content, and further in an amount sufficient to be uniformly interposed between silicon carbide particles. The reason why the amount of the carbonaceous additive added is set to 0.3 to 5.0 parts by weight in terms of fixed carbon content is that if it is less than 0.3 parts by weight, most of the carbonaceous additive will be consumed by oxygen. This is because the effect of optimizing diffusion cannot be sufficiently exerted, and on the other hand, if the amount exceeds 5.0 parts by weight, excessive carbon will exist between silicon carbide particles, significantly inhibiting sintering. The carbonaceous additive is added at least at the beginning of sintering.
Preferably, it has a specific surface area of 100 m ² /g. The reason for this is that if the specific surface area at the start of sintering is smaller than 100 m ² /g, the effect of optimizing the diffusion of SiC is weak, so in order to fully exhibit the effect of optimizing the diffusion of SiC, it is necessary to add a large amount. This is because the inclusion layer in the sintered body increases, making it difficult to obtain a high-strength sintered body. As the carbonaceous additive, any material that can cause carbon to be present at the start of sintering can be used, such as phenolic resin, lignin sulfonate, polyvinyl alcohol, cornstarch, molasses, coal tar pitch, alginate, and polyphenylene. various organic substances or carbon black,
Pyrolytic carbon such as acetylene black can be advantageously used. According to the present invention, silicon carbide fine powder, a boron-containing additive, and a carbonaceous additive are homogeneously mixed, then formed into a formed body having an arbitrary shape, and then sintered at 1700 to 2300°C in a non-oxidizing atmosphere. However, a silicon carbide sintered body having a density of 2.8 g/cm ³ or more is produced. According to the present invention, it is advantageous that the non-oxidizing atmosphere is a gas atmosphere consisting of at least one selected from argon, helium, neon, krypton, xenon, and hydrogen. By the way, during sintering in the present invention, as described above, CO gas is generated according to the above equations (1) and (2). If the CO gas is present in a large amount, the reaction of the above formula will be suppressed, and the silica film on the silicon carbide surface will not be removed sufficiently, making it impossible to obtain sufficient sintering shrinkage.
If the silica film remains, it will form an intervening phase within the silicon carbide sintered body and deteriorate the physical properties, especially the mechanical strength, of the sintered body, so the CO gas must be removed from the furnace. Therefore, according to the present invention, it is advantageous to provide the above-mentioned gas flow atmosphere inside the furnace. Note that it is advantageous to maintain the CO gas partial pressure in the furnace atmosphere during the sintering to 10 KPa or less. According to the present invention, the formed body is heated at 1700 to 2300°C.
It is necessary to sinter within the range of The reason for this is that when the sintering temperature is lower than 1700℃, the sintering temperature of 2.8g/cm ³ of the present invention is lower than 1700℃.
It is difficult to obtain a sintered body with a density higher than 2,300°C, and conversely, at temperatures higher than 2300℃, crystal grains grow significantly and the physical properties of the sintered body, such as mechanical strength, decrease. In order to obtain a sintered body with a fine structure and high strength, it is advantageous to sinter within a temperature range of 1900 to 2100°C. According to the present invention, in the temperature range of 1500 to 1700°C during the temperature increase process leading to the sintering temperature, the silica film removal reaction can be rapidly progressed to uniformly generate the neck formation reaction. It is advantageous to maintain the partial pressure of CO gas below 1 KPa in said temperature range for a sufficient period of time. Next, the present invention will be specifically explained with reference to Examples and Comparative Examples. Example 1 Silica sand powder (SiO ₂ = 99.6%, total Al = 0.1%, 80 mesh or less), anthracite powder (C = 87.8%, total Al =
0.4%, 325 mesh or less) and pitch powder (C
= 50.4%, 200 mesh or less, 7% by weight based on silica sand) was blended so that the C/SiO ₂ molar ratio was 3.8, and the mixture was placed in a vertical screw mixer and mixed for 10 minutes. While spraying a 0.5% CMC aqueous solution onto the above-mentioned blended raw materials, the mixture is molded using a dish-type granulator, sized using a sieve and Burr Grizzly, and then dried to obtain an average particle size.
A molding raw material of 10.5 mm and bulk specific gravity of 0.6 was obtained. The molding raw material was then charged from the top of a manufacturing apparatus similar to that described in Japanese Patent Publication No. 57-48485, and subjected to indirect electrical heating to carry out the SiC formation reaction at a temperature of about 1900°C. Furthermore, the obtained product was purified and classified for particle size to prepare silicon carbide fine powder. The silicon carbide fine powder is 96.7% β-type crystals and the rest is
It consists of 2H type crystal, and the lattice constant of β type crystal is
4.3609Å, 0.31% by weight aluminum,
It contained 0.32% by weight of free carbon, 0.18% by weight of oxygen, and had a specific surface area of 15.8 m ² /g. The lattice constant of the β-type crystal was determined from the (420) diffraction line. The silicon carbide fine powder is 99.9g and the specific surface area is 27.8m ² /
150 ml of acetone was added to a mixture of 0.1 g of boron carbide powder and 2.0 g of novolac type phenolic resin having a fixed carbon content of 51.6% by weight, and mixed for 2 hours using a vibrating mill. The mixture slurry was discharged from the vibration mill and spray-dried to obtain granules having an average particle diameter of 0.09 mm and a powder bulk density of 35% (1.12 g/cm ³ ). An appropriate amount of the granules was taken and pre-molded using a metal mold at a pressure of 0.15 t/cm ² , and then molded using a hydrostatic press at a pressure of 1.8 t/cm ² . The density of the formed body obtained by the above molding is 61%
(1.95g/cm ³ ). The formed body was placed in a Tammann type sintering furnace and sintered in an argon gas stream under atmospheric pressure. The temperature raising process was from room temperature to 1650°C at 5°C/min. After holding at 1650°C for 40 minutes, the temperature was further raised at 5°C/min and the maximum temperature was 2000°C and held for 30 minutes. The partial pressure of CO gas during sintering is 5KPa or less from room temperature to 1650℃, 0.5KPa or less when held at 1650℃, and at higher temperatures than 1650℃.
The argon gas flow rate was adjusted appropriately so that it was 5KPa or less. The obtained sintered body contains 0.31% by weight of aluminum,
It contained 1.0% by weight of free carbon and had a density of 3.12 g/cm ³ (98.0% relative theoretical density). In addition, as a result of powder X-ray diffraction measurement of this sintered body, this sintered body
It was found that 92.1% were β-type crystals. The sintered body was processed into a plate shape of 30×30×1 mm and washed with acetone to prepare a sample for oxidation resistance test. The sample was treated in a heating furnace maintained in an air atmosphere at 1400°C for 20 hours, and the weight increase before and after the treatment was measured, and the weight increase was 0.02 mg/cm ² compared to before treatment, indicating that the oxidation resistance was recognized as being excellent. Example 2, Comparative Example 1 Same as described in Example 1, but using oil coke powder with different aluminum content as shown in Table 1 instead of anthracite powder, and at the temperature shown in Table 1. A silicon carbide fine powder was prepared. The physical properties of the obtained silicon carbide fine powder are shown in Table 1. Using the silicon carbide fine powder shown in Table 1 above, sintered bodies were obtained in the same manner as in Example 1, except that the amount of boron carbide added was changed as shown in Table 1. The physical properties of the obtained sintered body were measured in the same manner as shown in Example 1, and are shown in Table 1.

【table】

[Table] According to Table 1, although Examples 2-1 and 2-2 differ in total Al content, high-density sintered bodies were obtained in both cases, and the oxidation resistance was also different. It turns out to be excellent. Furthermore, in Example 2-3, the SiC formation reaction temperature was particularly raised to 2100°C, and the obtained silicon carbide powder had a lattice constant of 4.3618 Å, and the sintered body produced from this powder had a particularly high density. It also had the best oxidation resistance. In Examples 2-4 and 2-5, the silicon carbide powder used in Example 1 was used, but the amounts of boron carbide added were changed to 0.05 g and 0.15 g, respectively, to produce sintered bodies. All of the obtained sintered bodies had high density and excellent oxidation resistance. On the other hand, in Comparative Example 1, the average value of the lattice constant of the silicon carbide powder crystal is 4.3580 Å, the density of the sintered body manufactured using this is as low as 2.72 g/cm ³ , and the oxidation resistance is also lower than that of the example. It was extremely inferior compared to Example 3 As starting materials, 99.9 g of the silicon carbide fine powder described in Example 1 and the boron carbide powder described in Example 1 were further classified by particle size, and 0.1 g of boron carbide was prepared to have a specific surface area of 47.8 m ² /g. Particle size 210Å, specific surface area
150 ml of acetone and polyethylene glycol to a mixture of 1.5 g of carbon black at 128 m ² /g.
After adding 0.7 ml and ball milling for 10 hours, the slurry was spray dried. An appropriate amount of this dry powder was collected and a green body was prepared in the same manner as in Example 1 to obtain a sintered body. The density of the obtained sintered body is as high as 3.01g/ ^cm3 .
It was found that 94.0% were β-type crystals. Further, the weight increase in the oxidation resistance test measured in the same manner as in Example 1 was as small as 0.03 mg/cm ² and the oxidation resistance was excellent. Example 4 α was produced in the same manner as in Example 1, but by pulverizing, refining, and classifying commercially available α-type silicon carbide into 60 parts by weight of the silicon carbide fine powder described in Example 1 as a starting material.
A sintered body was obtained using silicon carbide fine powder mixed with type silicon carbide fine powder at a ratio of 40 parts by weight. Note that the α-type silicon carbide fine powder has a specific surface area of 14.8.
m ² /g, and contained 0.1% by weight of aluminum, 0.3% by weight of free carbon, and 0.2% by weight of oxygen. The density of the obtained sintered body was 2.90 g/cm ³ and the content of β-type silicon carbide was 40.4%. Further, the weight increase in the oxidation resistance test measured in the same manner as in Example 1 was as small as 0.04 mg/cm ² , indicating excellent oxidation resistance. As described above, according to the present invention, a pressureless sintered body of silicon carbide having high density and excellent oxidation resistance can be manufactured at low cost.

Claims (1)

[Claims] 1. A method for producing a silicon carbide sintered body by pressure-free sintering of silicon carbide fine powder, which contains 50% by weight or more of β-type silicon carbide having an average crystal lattice constant of 4.3584 Å or more. silicon carbide fine powder
0.01 to 0.25 in terms of 100 parts by weight and boron content
After homogeneously mixing part by weight of a boron-containing additive with a carbonaceous additive in an amount of 0.3 to 5.0 parts by weight in terms of fixed carbon content, the mixture is formed into a formed body having an arbitrary shape,
A method for producing a silicon carbide sintered body, which comprises then sintering at 1700 to 2300°C in a non-oxidizing atmosphere to produce a silicon carbide sintered body having a density of 2.8 g/cm ³ or more. 2. The method according to claim 1, wherein the β-type silicon carbide is a β-type silicon carbide obtained by firing silica and carbon at a high temperature as starting materials. 3 The β-type silicon carbide contains aluminum from 0.02 to
The method according to claim 1 or 2, wherein the content is 1.0% by weight. 4. The silicon carbide fine powder has a specific surface area of 5 to 50 m ² /g.
The method according to any one of claims 1 to 3. 5. The method according to any one of claims 1 to 4, wherein the silicon carbide fine powder has an oxygen content of 0.1 to 1.0% by weight. 6. The boron-containing additive is at least one selected from boron, boron carbide, or mixtures thereof.
6. The method according to any one of claims 1 to 5, which is a species. 7 The carbonaceous additive must be at least 100% at the start of sintering.
The method according to any one of claims 1 to 6, which has a specific surface area of m ² /g. 8. The method according to any one of claims 1 to 7, wherein at least 20% by weight of the silicon carbide sintered body is β-type silicon carbide.